Method of forming a pattern using proximity-effect-correction

ABSTRACT

A method of correcting light proximity effects includes the steps of: compressing design data of a circuit pattern (step S 1 ); generating a projection image which is formed during a process of transferring a pattern onto a wafer, the projection image being generated according to the design data (step S 2 ); predicting the size of the transferred pattern, said prediction being performed from the projection image (step S 3 ); calculating the difference between the predicted size of the transferred pattern and the pattern size designated by the design data (step S 4 ); correcting the compressed design data by an amount equal to the above-described difference (step S 5 ); judging whether the correction amount is within an allowable range (step S 6 ); expanding the corrected data after the correction amount has fallen within the allowable range (step S 7 ); and outputting the resultant data (step S 8 ).

This disclosure is a division of patent application Ser. No. 08/529,177,filed on Sep. 15, 1995 now U.S. Pat No. 5,815,685.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a system and method for correctingpattern data of an integrated circuit or the like so as to cancel thelight proximity effects. The present invention also relates to a methodof forming a pattern using such a method for correcting the lightproximity effects.

2. Description of the Related Art

Referring to FIGS. 29A to 29D, a conventional LSI production processwill be described below. First, an LSI pattern such as that shown inFIG. 29A is designed using a CAD system or a similar tool andcorresponding LSI pattern data is produced. The designed LSI patternincludes a plurality of rectangular patterns 291. Electron beam exposureis then performed according to the designed pattern data so as toproduce a mask including a plurality of patterns 292 as shown in FIG.29B. A wafer is exposed to ultraviolet light through the mask therebytransferring the pattern 292 formed on the mask onto the wafer. However,the pattern transferred to the wafer becomes different from the maskpattern consisting of rectangular patterns 292 owing to diffraction oflight in that corners of rectangles are rounded as shown in FIG. 29C. Ifthe wafer is etched or subjected to a similar process using thetransferred pattern 293, then the resultant pattern 294 formed on thewafer has further deformation due to the micro coding effect as shown inFIG. 29D. If the wafer is then subjected to an oxidation process to forma local oxidation of silicon (LOCOS); isolation structure, the patternis deformed further owing to the so-called bird's beak effect.

In production of an integrated circuit such as an LSI, the patterndeformation accumulates via a series of various production processes asdescribed above, and the actual size of the pattern obtained at the endof the production processes is generally different from the designedsize.

In recent years, with the reduction in the size of patterns ofintegrated circuits, it is required to control the pattern size moreprecisely. In practice, however, there occurs pattern deformation suchas that described above during production processes, and electricalcharacteristics of devices and various margins are influenced by thepattern deformation to a degree that cannot be neglected.

SUMMARY OF THE INVENTION

It is a general object of the present invention to solve the problemsdescribed above. More specifically, it is an object of the presentinvention to provide a light proximity effect correction apparatus andmethod for alleviating the deformation of patterns due to lightproximity effects~ during production processes of an integrated circuit.

It is another object of the present invention to provide a method offorming a pattern according to such a method of correcting for lightproximity effects.

According to a first aspect of the present invention, there is provideda light proximity correction system including: a design data input unitfor inputting design data of a circuit pattern; a data compression unitfor compressing the design data input via the design data input unit; anoptical image formation unit for forming an optical projection imageused to transfer a pattern onto a wafer according to the design datainput via the design data input unit; a prediction unit for predictingthe size of the pattern which will be transferred onto the wafer, theprediction being performed on the basis of the projection image formedby the optical image formation unit; a comparison unit for calculatingthe difference between the size of the transferred pattern predicted bythe prediction unit and the size of the pattern designated by the designdata input via the design data input unit; a correction unit forcorrecting the design data compressed by the data compression unit by anamount equal to the difference determined by the comparison unit; a dataexpansion unit for expanding the data corrected by the correction unit;and a corrected data output unit for outputting the data expanded by thedata expansion unit.

According to a second aspect of the present invention, there is provideda light proximity correction method, including the steps of: compressingdesign data of a circuit pattern; forming an optical projection imageused to transfer a pattern onto a wafer according to the design data;predicting the size of the pattern which will be transferred onto thewafer, the prediction being performed on the basis of the projectionimage formed in the previous step; correcting the design data by anamount equal to the difference between the predicted size of thetransferred pattern and the size of the pattern designated by the designdata; expanding the corrected data; and outputting the expanded data.

According to a third aspect of the present invention, there is provideda method of forming a pattern, including the steps of: correcting thelight proximity effect which occurs during a process of transferring apattern onto a wafer, the correction of the light proximity effect beingperformed on the basis of design data of a circuit pattern, therebygenerating corrected data; performing electron beam exposure accordingto the corrected data thereby producing a mask pattern; performing lightexposure through the mask pattern thereby transferring the mask patternonto a wafer; and processing the wafer using the transferred maskpattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1E are schematic representations of a series of processingsteps of forming a pattern according to a first embodiment of thepresent invention;

FIG. 2 is a block diagram of a light proximity correction systemaccording to a second embodiment of the present invention;

FIG. 3 is a flow chart illustrating an operation relating to the secondembodiment of the present invention;

FIG. 4 is a block diagram of a light proximity correction systemaccording to a third embodiment of the present invention;

FIG. 5 is a flow chart illustrating an operation relating to the thirdembodiment of the present invention; FIGS. 6, 7A, and 7B are schematicrepresentations of correction methods according to fourth and fifthembodiments, respectively, of the present invention;

FIGS. 8A8B, 9A, 9B, 10A, 10B, 10C, 11, 12A, 12B, 13A and 13B areschematic representations of correction methods according to seventh totwelfth embodiments, respectively, of the present invention;

FIGS. 14 and 15 are block diagrams of an optical image calculation unitand an optical image measurement unit, respectively, of a correctionsystem according to a third embodiment of the present invention;

FIG. 16 is a schematic representation of a correction method accordingto a twenty-second embodiment of the present invention;

FIGS. 17A17B, 18A and 18B are schematic representations of a correctionmethod according to a twenty-third embodiment of the present invention;

FIGS. 19A19B, 20 AND 21 are schematic representations of correctionmethods according to twenty-seventh to twenty-ninth embodiments,respectively, of the present invention;

FIGS. 2223A, 23B, 24A, 24B, 25, 26A, 26B, 27A, 27B, 28A and 28B areschematic representations of correction methods according tothirty-third to thirty-ninth embodiments, respectively, of the presentinvention;

FIGS. 29A to 29D are schematic representations of a series of processingsteps of forming a pattern according to a conventional technique;

FIG. 30 is a schematic representation of a correction method accordingto the thirteenth embodiment of the present invention;

FIG. 31 is a schematic representation of a correction method accordingto the fourteenth embodiment of the present invention;

FIG. 32 is a schematic representation of a correction method modifiedfrom the fourteenth embodiment of the present invention;

FIGS. 33 and 34 are schematic representations of a correction methodaccording to a twenty-fourth embodiment of the present invention;

FIGS. 35A35B and 36 are schematic representations of correction methodsaccording to twenty-fifth and twenty-sixth embodiments, respectively, ofthe present invention;

FIGS. 37A37B, 38A, 38B, 39, 39B and 39C are schematic representations ofcorrection methods according to thirtieth and thirty-second embodiments,respectively, of the present invention;

FIGS. 40A40B and 40C are schematic representations of a correctionmethod according to a forty-second embodiment of the present invention;

FIGS. 41A41B, 41C, 41D, 42A, 42B, 43A, 43B, 44A and 44B are schematicrepresentations of a correction method according to a sixth embodimentof the present invention;

FIG. 45 is a schematic representation of a correction method accordingto a fifteenth embodiment of the present invention;

FIG. 46 is a schematic representation of a correction method modifiedfrom the fifteenth embodiment of the present invention;

FIGS. 47 and 48 are schematic representations of correction methodsaccording to a sixteenth and seventeenth embodiments, respectively, ofthe present invention;

FIG. 49 is a schematic representation of a correction method accordingto an eighteenth embodiment of the present invention;

FIG. 50 is a schematic representation of a correction method modifiedfrom the eighteenth embodiment of the present invention;

FIG. 51 is a schematic representation of a correction method accordingto a nineteenth embodiment of the present invention;

FIG. 52 is a schematic representation of a correction method accordingto a twentieth embodiment of the present invention;

FIG. 53 is a schematic representation of a correction method modifiedfrom the twentieth embodiment of the present invention; and

FIG. 54 is a schematic representation of a correction method accordingto a forty-first embodiment of the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, preferred embodiments of thepresent invention will be described below.

EMBODIMENT 1

FIGS. 1A-1E are schematic diagrams illustrating a series of processingsteps for forming a pattern according to a first embodiment of thepresent invention. First, an LSI pattern such as that shown in FIG. 1Ais designed using a CAD system or a similar tool so as to producecorresponding LSI pattern data consisting of a plurality of rectangularpatterns 11. The designed data is then corrected according to the lightproximity correction method which will be described in detail later soas to obtain light-proximity-corrected data as shown in FIG. 1B. Thelight-proximity-corrected data consists of a plurality of patterns 12corresponding to the plurality of rectangular patterns 11 in the designdata wherein each pattern 12 has auxiliary patterns 121 added at eachcorner so as to correct for pattern deformation due to diffraction oflight which occurs during a process for transferring the pattern onto awafer.

Electron beam exposure is then performed using thelight-proximity-corrected data so that a mask including a plurality ofpatterns 13 is produced as shown in FIG. 1C. A wafer is then exposed toultraviolet light through this mask thereby transferring the patterns 13formed on the mask onto the wafer. As a result, as shown in FIG. 1D,patterns 14 are formed on the wafer in such a manner that the auxiliarypatterns disposed at four corners at each rectangle are removed as aresult of diffraction of light and thus the resultant shape of eachpattern 14 becomes a rectangle.

If the wafer is etched using the transferred patterns 14, the etchedpatterns 15 become such as those shown in FIG. 1E. Although the etchedpatterns 15 differ from the transferred patterns 14 shown in FIG. 1Dowing to the micro loading effect, the deformation is much smaller andthus the pattern is much closer to the design pattern than in the caseof the pattern 294 shown in FIG. 29D which is formed according to theconventional technique. Whereas additional deformation occurs in thepattern when the wafer is further subjected to an oxidation process toform a LOCOS isolation structure, the final pattern has higher accuracythan the pattern formed according to the conventional technique.

EMBODIMENT 2

FIG. 2 is a block diagram illustrating a light proximity correctionsystem used to accomplish the light proximity correction in the patternformation process described in the first embodiment. Design data of anintegrated circuit pattern produced with a CAD system is input to thesystem via a design data input unit 1. The design data input unit 1 isconnected to a data compression unit 2 which performs data compression,in an pre-processing step, on the input data. The output of the datacompression unit 2 is connected to an optical image calculation unit 3for calculating an image which will be projected onto a wafer in apattern transfer process. The output of the optical image calculationunit 3 is connected to a pattern prediction unit 4 for predicting thepattern which will be formed in-a resist as a result of the patterntransfer process. The pattern prediction unit 4 and the design datainput unit 1 are connected to a comparison unit 5 for comparing thepredicted pattern with the design data. The output of the comparisonunit 5 is connected to a correction unit 6 for light proximitycorrection. The output of the correction unit 6 is connected to adetermination unit 7 for determining whether the correction amount iswithin an allowable range. The output of the unit 7 is connected to adata expansion unit 8 for expanding the data. The output of the dataexpansion unit 8 is connected to a correction data output unit 9. Theoutput of the unit 7 is also connected to the optical image calculationunit 3. The optical image calculation unit 3 serves as an optical imageformation unit defined above in the first aspect of the invention.

FIG. 3 is a flow chart illustrating the correction method using thelight proximity correction system described above. Design data producedwith a CAD system or the like is input via the design data input unit 1,and then compressed by the data compression unit 2 in a pre-processingstep (step S1). The optical image calculation unit 3 then calculates animage which will be projected onto a wafer from the compressed data(step S2). Furthermore, on the basis of the calculated image to beprojected, the pattern prediction unit 4 predicts the size of a patternwhich will be finally obtained after a pattern transfer process (stepS3). The comparison unit 5 compares the predicted pattern size with thesize of the design pattern which was input via the design data inputunit 1, and outputs a correction amount which is a difference betweenthe predicted pattern size and the design value (step S4). Thecorrection unit 6 corrects the compressed data according to thecorrection amount given by the comparison unit 5 (step S5).

Then the determination unit 7 determines whether the correction amountis within the predefined allowable range (step S6). If the correctionamount is not within the allowable range, it is considered that thecorrection is not good enough, and thus the process returns to step S2so as to calculate the projection image again and correct the data againin steps S3 to S5. Steps S2 to S6 are performed repeatedly until thecorrection value falls within the allowable range. If it is concluded instep S6 that the correction amount has fallen within the allowablerange, it is considered that the light proximity correction is properlycompleted. Thus the data expansion unit 8 expands the data (step S7) andthe corrected data is output via the correction data output unit 9 (stepS8). The corrected data is input to an electron beam exposure apparatus(not shown) for producing a mask.

Since data correction is performed according to the result of comparisonbetween the predicted pattern and the design pattern after the data iscompressed by the data compression unit 2, a reduction in the correctioncalculation time is achieved. Furthermore, data correction is performedrepeatedly until the correction amount falls within the allowable rangeso that the final pattern size has a required accuracy.

EMBODIMENT 3

FIG. 4 is a block diagram of a light proximity correction systemaccording to a third embodiment of the present invention. This systemaccording to the third embodiment is the same as that according to thefirst embodiment shown in FIG. 2 except that the optical imagecalculation unit 3 is replaced by an optical image measurement unit 10serving as the optical image formation unit defined in the first aspectof the invention. The optical image measurement unit 10 includes anoptical system for measuring the image projected onto a wafer via a maskproduced according to the design data. In the case of the secondembodiment described above, the pattern image which will be projectedonto a wafer is calculated in step S2 by means of software with theoptical image calculation unit 3 from the compressed data. In the thirdembodiment, however, the projected image is measured by means ofhardware with the optical image measurement unit 10 in step S9 after thedata compression in step S1, as shown in FIG. 5. In FIG. 5, steps S1, S3to S8 are the same as the corresponding steps of the second embodiment.

The optical system of the optical image measurement unit 10 isconstructed so that the requirements described below are satisfied:

λ1=λ2; σ1=σ2; m 1·NA 1=m 2·NA 2

where λ1, σ1, m1, and NA1 are parameters relating to a stepper(step-and-repeat projection tool) wherein λ1 is the wavelength of light,σ1 is the spatial coherence, m1 is the magnification, and NA1 is thenumerical aperture, and λ2, σ2, m2, and NA2 are parameters relating tothe optical system of the optical image measurement unit 10 wherein λ2is the wavelength of light, σ2 is the spatial coherence, m2 is themagnification, and NA2 is the numerical aperture. The employment of suchan optical system allows high accuracy measurement of the diffractioneffects of light arising in the pattern transfer process and it ispossible to reduce the time required to perform the correction process.

EMBODIMENT 4

In-the data compression process in the second or third embodiment, thedata compression unit 2 may divide the design data into a plurality ofdata blocks 6 a to 6 i as shown in FIG. 6 so that optical proximitycorrection is performed separately for each of the data blocks. In thecase where the design data is divided into a plurality of data blocks, abuffer area is disposed around each data block so that the influence ofpattern elements in neighboring data blocks can be taken into accountvia the buffer areas in the correction of pattern elements included ineach data block. In FIG. 6, for example, there is a buffer area 60 earound a data block 6 e. It is determined whether the buffer area 60 eincludes some pattern elements that can have proximity effects onpattern elements in the data block 6. According to the result, it isdecided which side of the data block 6 e should be corrected. Thistechnique allows each data block to be corrected separately and thusmakes it possible to independently perform light proximity correction ona plurality of data blocks at the same time in a parallel fashionthereby reducing the time required for the correction process.

EMBODIMENT 5

The data compression unit 2 calculates the distance between opposingsides for every pattern element in each data block described in thefourth embodiment so as to check whether there is a data block whichincludes sides the distance between which is less than a predeterminedthreshold. If it turns out that some data blocks include such sides,then those data blocks are subjected to the correction process whereasdata blocks including no such sides are not subjected to the correctionprocess. In the example of a data block shown in FIG. 7A includingpatterns 7 a and 7 b, whereas the distance A is large, distances B and Care smaller than the threshold, and thus light proximity correctionshould be performed on this data block. Therefore, this data block issubjected to the correction process. In contrast, in the case of a datablock shown in FIG. 7B, the distance A of a pattern element 7 c is longenough and there are no opposite sides located nearer to each other thanthe threshold, and thus it is concluded that this data block needs nocorrection. As a result, no correction is performed on this data block.In this embodiment, it is determined whether correction is required foreach data block and thus it is possible to reduce the time required forthe correction process.

EMBODIMENT 6

In the case where an exposure system including a variable light sourceis employed, a light shielding part is disposed in a secondary lightsource plane and therefore a diffraction image of the light source isformed on the pupil plane of the exposure apparatus. For example, FIG.41A illustrates a diffraction pattern of a variable light source havinga light shielding part in the form of straight lines, and FIG. 41Billustrate a diffraction pattern of a variable light source having alight shielding part in the form of crosses. In FIGS. 41A and 41B, thediffraction patterns are of a zeroth-order light source image 411 or 421and first-order light source images 412 or 422 formed on the pupil plane410 These figures describe diffraction patterns under the criticalconditions where two-light-ray interference occurs between thezeroth-order light source image 411 or 421 and either one of twofirst-order light source images 412, 422.

The period L2 corresponding to the cutoff frequency of the two-light-rayinterference can be described as follows:

L2=λ/(σ+1)NA

where λ is the wavelength of light, σ is the spatial coherence, and NAis the numerical aperture. That is, if the size of a pattern is greaterthan the period L2, then at least two light rays can interfere with eachother.

FIGS. 41C and 41D illustrate diffraction patterns of variable lightsources having light shielding parts in the forms of straight lines andcrosses, respectively, for the cases of critical conditions in whichthree-light-ray interference occurs among the zeroth-order light sourceimage 411 or 421 and first-order light source images 412 and 413 or 422and 423 formed on the pupil plane 410. The period L3 corresponding tothe cutoff frequency of the three-light-ray interference can bedescribed as follows:

L 3=λ/(1−σb)NA

where σb is the spatial coherence of the light source image associatedwith the light shielding part. Thus if the pattern size is greater thanthe period L3, three-light-ray interference occurs.

FIG. 42A illustrates the light proximity effects on the final width oflines having a width of 0.35 μm for various spacing widths when a normallight source is used, and FIG. 42B illustrates the light proximityeffects on the finally-obtained width of spaces having a width of 0.35μm for various line widths. In FIGS. 42A and 42B, “small” denotes apattern having a size smaller than the period L2. The conditions areadjusted using a “small” pattern so that the finally-obtained line andspace widths of such small patterns are maintained unchanged withoutbeing influenced by the light proximity effects. The “middle” patternrefers to a pattern having a size in the range from the period L2 to L3,and the “large” pattern refers to a pattern having a size greater thanthe period L3. In the cases of these patterns, the finally-obtained lineand space widths become different from the design values. Therefore,light proximity correction is required for the conditions where the lineor space width is equal to the “middle” or “large” pattern, asrepresented by symbols X in FIG. 44A.

FIGS. 43A and 43B illustrate light proximity effects for cases where avariable light source is used. Also in these cases, “small”, “middle”,and “large” patterns refer to those patterns having sizes less than theperiod L2, in the range from the period L2 to L3, and greater than theperiod L3, respectively, as in the case of the normal light source. Theconditions are also adjusted using a “small” pattern so that thefinally-obtained line and space widths of such small patterns aremaintained unchanged without being influenced by the light proximityeffects. In the variable light source, as can be seen from FIG. 43A, thefinally-obtained width of lines with spaces corresponding to the“middle” pattern which can have two-light-ray interference are alsomaintained unchanged without being influenced by the light proximityeffects. However, the final widths of patterns having other sizesdeviate from the design values. Thus, the light proximity correction isrequired when the line width is equal to that of the “middle” or “large”pattern, and the space width is equal to that of the “large” patternwhereas the light proximity correction is not required when the spacewidth is equal to that of the “middle” pattern, as represented bysymbols O in FIG. 44B.

Therefore, when a variable light source is employed, light-maskingpatterns having a size less than the period L3 corresponding to thecutoff frequency of the three-light-ray interference may be consideredto require no correction in the data compression process.

Furthermore, the finally-obtained widths of lines with spacescorresponding to the “large” pattern have a substantially constantdeviation as shown in FIG. 43A. As a result, when those patterns havinga size less than a value defining a threshold requiring the lightproximity correction, and the opposite sides are located at an intervalgreater than the period L3 corresponding to the three-light-rayinterference cutoff frequency, correction for these patterns can beeasily performed simply by adding a constant correction value to thepattern sizes.

EMBODIMENT 7

In the data compression process, if a pattern element has a large sizelying across a plurality of data blocks as shown in FIG. 8A, only thosedata blocks including a part of a side of the pattern element aresubjected to the correction process. Those data blocks including no sideof the pattern element are not subjected to the correction processbecause light proximity effects cannot occur in such data blocks. Thus,those data blocks which require no correction can be skipped in thecorrection process. As a result, a great reduction in the correctiontime is achieved.

EMBODIMENT 8

In the data compression process, if a plurality of data blocks includean identical pattern element only one of them is subjected to thecorrection process, and the others are skipped in the correctionprocess. For example, in the example shown at the top of FIG. 9A, arectangle extends in a horizontal direction across data blocks 9 a to 9e, and the blocks 9 b, 9 c, and 9 d include a pattern element identicalto each other. In this case, as shown in FIG. 9B, only the data block 9b of the data blocks 9 b to 9 d is subjected to the correction process.After the completion of the correction process, the correction result isapplied to data blocks 9 c and 9 d. Thus, in this embodiment, when apattern such as that shown in FIG. 9A is given, it is required tocorrect only the data blocks 9 a, 9 b, and 9 e -9 m.

As a result, the time required for the correction process can bereduced.

EMBODIMENT 9

In the data compression process, if a pattern to be processed includesan array consisting of a plurality of identical cells arranged side byside, one cell, for example, a cell 100 shown in FIG. 10A, selected fromthe array is first subjected to a light proximity correction process sothat a corrected pattern 101 is obtained as shown in FIG. 10B, and thenthe corrected pattern is expanded into an array form in such a manner asshown in FIG. 10C. This technique makes it possible to reduce the timerequired for the correction process.

EMBODIMENT 10

When the pattern to be processed is a memory cell array consisting of amemory cell pattern 110 arranged in a periodic fashion as shown in FIG.11, the pattern is divided into data blocks 11 a in the data compressionprocess in such a manner that the divided blocks 11 a have a periodcorresponding to the period of the memory cell pattern. This allows useof periodic boundary conditions and thus there is no need to use bufferareas as opposed to the embodiment described in connection with FIG. 6.Furthermore, the period allows effective use of fast Fouriertransformation (FFT) and thus a further reduction in the processing timecan be achieved.

EMBODIMENT 11

In the case where a data block includes a plurality of pattern elements121 to 125 lying adjacent to each other as shown in FIG. 12A, thesepattern elements 121 to 125 are combined into one pattern element in theform of a polygon 126 in the data compression process, as shown in FIG.12B. This allows the data to be compressed more effectively so thatredundant sides included in a pattern are removed and thus redundantcorrection processes are prevented.

EMBODIMENT 12

In the case where a data block includes a plurality of pattern elements131 to 137 surrounding a space pattern as shown in FIG. 13A, the datacompression process describes the pattern using a pattern element 138which defines the outer periphery of the whole pattern including thepattern elements 131 to 137 and also using pattern elements 139 a and139 b which define inner space patterns, as shown in FIG. 13B. Thismakes it easier to perform the correction process on a pattern includinga space pattern inside it.

EMBODIMENT 13

The optical image calculation unit 3 shown in FIG. 2 may be formed witha plurality of CPUs 141 to 145 connected to each other in a parallelfashion as shown in FIG. 14. The design data which has been compressedby the data compression unit 2 is divided into a plurality of portionsand each portion is processed in parallel by CPUs 141-145. Thecalculation results are finally integrated so as to obtain completecorrection data. The parallel processing according to the presentembodiment results in a great reduction in the time required for theprocessing. For example, if five CPUs are used as shown in FIG. 14, theprocessing speed becomes five times faster than that of a systemincluding only one CPU.

Alternatively, the CPU 141 may be used as a master processor whichserves as the data compression unit 2, the data expansion unit 8, andthe correction data output unit 9 shown in FIG. 2, while the CPUs142-145 may be used as slave processors which serve as the optical imagecalculation unit 3, the pattern prediction unit 4, the comparison unit5, the correction unit 6, and the unit 7 shown in FIG. 2. In this case,the processing is performed according to a procedure shown in FIG. 30.First, CAD data representing a mask pattern is input as design data tothe master processor. The master processor divides the received CAD datainto a plurality of data blocks and compresses the data of each datablock in such a manner that there is no redundancy in the data. Themaster processor then creates buffer areas around individual datablocks. Then, data representing optical characteristics of an exposuresystem (not shown) as well as an exposure result of a reference patternare input to the master processor. From the exposure result of thereference pattern, the master processor determines the relationshipbetween the reference pattern and its optical image. In particular thelight intensity threshold is set so that pattern prediction can beproperly performed. The master processor also performs calculationswhich are common for all data blocks, and transmits the calculationresults as well as the relationship described above to the plurality ofslave processors.

The master processor establishes synchronization with the slaveprocessors and then waits for a signal transmitted by a slave processor.Upon reception of a ready-to-start signal transmitted by a slaveprocessor, the master processor transmits a start-of-process commandtogether with data of a data block to be processed by the slaveprocessor to the slave processor. If the master processor receives anend-of-calculation signal from a slave processor, the master processorreceives a calculation result from that slave processor and stores it.When all data has been processed, the master processor sends anend-of-process command to all slave processors so as to complete the allprocesses. On the other hand, if there is still data which has not beenprocessed, the master processor waits for another signal transmittedfrom a slave processor.

When slave processors receive a start-of-process command and data of anassigned data block from the master processor, the slave processorsperform a calculation regarding an optical image and then perform acorrection relating to it. If the correction amount falls within theallowable range, then the slave processors compress the corrected dataand transmits the calculation results, together with anend-of-calculation signal to the master processor.

In this embodiment, the outermost loop in the flow chart shown in FIG. 3is performed in parallel by a plurality of slave processors and thus agreat reduction in the processing time is achieved.

EMBODIMENT 14

In the thirteenth embodiment described above, the relationship betweenthe reference pattern and the optical image thereof may be determined asfollows. First, as shown in FIG. 31, the size of a resist pattern whichis formed by actually performing exposure of the reference pattern ismeasured. The master processor calculates the optical image of thereference pattern determined from the reference mask data and retrievesthe optical intensity Ix at an edge of the reference pattern. Then, themaster processor determines the deviation Δ of the measured size of theresist pattern from the size of the reference pattern, and retrieves thelight intensity Iy of the optical image of the reference pattern at theposition where the above-described deviation occurs. The masterprocessor further determines the relationship between the lightintensities Ix and Iy by means of the least squares fitting method. Theslave processors determine threshold values which depend on the lightintensities Ix at edges using the relationship determined by the masterprocessor, and perform correction processing using the threshold values.

This technique allows the system to flexibly deal with variations in theresist process for various types of resists. As a result, it is possibleto perform high accuracy correction for various resist processconditions and for various types of resists.

In an alternative mode, the size of the resist pattern may be replacedby the size of the etched pattern formed by an etching process after theexposure of the reference pattern, as shown in FIG. 32. In this case,the variations arising during the etching process may also beincorporated in the correction and thus more precise correction can beachieved.

EMBODIMENT 15

In the thirteenth embodiment described above, instead of using therelationship between the reference pattern and the optical imagethereof, the relationship between the reference mask data and theproduced mask pattern may be used. In this case, as shown in FIG. 45,the reference pattern is first formed by electron beam exposure with thereference mask data and the size of resultant reference pattern ismeasured. The master processor calculates an electron beam exposurepattern from the reference mask data and retrieves the electron beamexposure pattern Ix near a mask edge of the electron beam exposurepattern. Then, the master processor determines the deviation Δ of themeasured size of the reference pattern from the size of the electronbeam exposure pattern, and retrieves the electron beam exposure patternIy at the position where the deviation Δ occurs. The master processordetermines the relationship between Ix and Iy by means of the leastsquares fitting method. The slave processors determine threshold values,which depend on the electron beam exposure pattern Ix near the edge,using the relationship determined by the master processor, and performcorrection processing using the threshold values.

According to the present embodiment, it becomes possible to evaluateonly the proximity effect arising when the electron beam exposure of amask is performed, separately from the other proximity effects, andincorporate this proximity effect in the correction process.

Alternatively, as shown in FIG. 46, the electron beam exposure may bereplaced by laser beam exposure. In this case, the relationship betweenthe reference pattern formed by laser beam exposure using the referencemask data and the laser beam exposure pattern calculated from thereference mask data is determined so that only the proximity effectrelating to the laser beam exposure of a mask can be evaluatedseparately from the other proximity effects and it can be incorporatedin the correction process.

EMBODIMENT 16

In the thirteenth embodiment described above, instead of using therelationship between the reference pattern and the optical imagethereof, the relationship between the pattern size of the referencepattern and the size of a resist pattern which is formed by actuallyexposing a resist to the reference pattern may be used. In this case, asshown in FIG. 47, for example, a reference pattern obtained according tothe fifteenth embodiment is used to expose a resist so as to form aresist pattern, and the size of the resultant resist pattern ismeasured. The master processor calculates an optical image from thepattern size obtained by measuring the reference mask data and retrievesthe optical image Ix near a mask edge of the optical image. The masterprocessor determines the difference Δ between the measured size of theresist pattern and the size of the reference pattern, and then retrievesthe optical image Iy at the position at which the difference Δ occurs.Furthermore, the master processor determines the relationship between Ixand Iy by means of the least squares fitting method. The slaveprocessors determine threshold values, which depend on the optical imageIx in an adjacent area, using the relationship determined by the masterprocessor, and perform correction processing using the above thresholdvalues.

In this embodiment, the proximity effect that occurs when a mask patternis transferred onto a wafer can be evaluated separately from the otherproximity effects and this effect can be incorporated in the correctionprocess.

EMBODIMENT 17

In the thirteenth embodiment described above, instead of using therelationship between the reference pattern and the optical imagethereof, the relationship between the size of a resist pattern and thesize of an etching pattern formed by performing an etching process usingthe resist pattern may be used. In this case, as shown in FIG. 48, anetching pattern is formed by actually performing an etching processusing a reference resist pattern obtained according to, for example, thesixteenth embodiment, and the size of the etching pattern obtained ismeasured. The master processor calculates an etching pattern from thepattern size obtained by measuring the reference resist pattern, andretrieves the etchant concentration Ix near the resist edge. Then, themaster processor determines the deviation Δ of the measured size of theetching pattern from the size of the reference resist pattern, andretrieves the etchant concentration Iy at the position where thedeviation Δ occurs. The master processor determines the relationshipbetween Ix and Iy by means of the least squares fitting method. Theslave processors determine threshold values, which depend on the etchantconcentration Ix in an adjacent region, using the relationshipdetermined by the master processor, and perform correction processingusing the threshold values.

In this embodiment, the micro loading effect that occurs during anetching process can be evaluated separately from the other effects andthis effect can be incorporated in the correction process.

EMBODIMENT 18

In the thirteenth embodiment described above, instead of using therelationship between the reference pattern and the optical imagethereof, it is possible to employ the relationship between referencemask data, and a resist pattern obtained by transferring a mask patternformed by electron beam exposure according to the reference mask data.In this case, as shown in FIG. 49, a reference pattern is formed byactually performing electron beam exposure according to the referencemask data, and a resist pattern is then formed by exposing a resist tothe obtained reference pattern. The size of the obtained resist patternis then measured. The master processor calculates an electron beamexposure pattern from the reference mask data, and further calculates anoptical image. Then, the master processor retrieves the optical image Ixnear a mask edge of the optical image. The master processor determinesthe deviation Δ of the measured size of the resist pattern from thereference mask data, and then retrieves the optical image Iy at theposition where the deviation Δ occurs. The master processor determinesthe relationship between Ix and Iy by means of the least squares fittingmethod. The slave processors determine threshold values, which depend onthe optical image Ix in an adjacent region, using the relationshipdetermined by the master processor, and perform correction processingusing the above threshold values.

In this embodiment, complex effects, of the electron beam proximityeffect which occurs when electron beam exposure is performed accordingto the reference mask data, and the light proximity effect, which occurswhen the mask pattern is transferred onto a wafer by means of opticallithography, can be evaluated, and these effects can be incorporatedinto the correction process.

In a modified mode of the present embodiment, as shown in FIG. 50, theelectron beam exposure may be replaced by laser beam exposure. In thiscase, a reference pattern is formed by actually performing laser beamexposure according to the reference mask data, and a resist pattern isthen formed by exposing a resist to the obtained reference pattern.Then, the relationship between the resist pattern and an optical imagecalculated from a laser beam exposure pattern, which is calculated fromthe reference mask data, is determined. In this modified mode, complexeffects of the laser beam proximity effect which occurs when the laserbeam exposure is performed according to the reference mask data, and thelight proximity effect, which occurs when the mask pattern istransferred onto a wafer by means of optical lithography, can beevaluated, and these effects can be incorporated into the correctionprocess.

EMBODIMENT 19

In the thirteenth embodiment, instead of using the relationship betweenthe reference pattern and the optical image thereof, the relationshipbetween the size of a reference pattern and the size of an etchingpattern formed by performing an etching process using a resist patternformed by exposing a resist to the reference pattern may be used. Inthis case, as shown in FIG. 51, a resist pattern is formed by actuallyexposing a resist to a reference pattern obtained according to, forexample, the fifteenth embodiment, and an etching pattern is then formedby performing an etching process using the obtained resist pattern. Thepattern size of the resultant etching pattern is then measured. Themaster processor calculates an optical image from a pattern sizeobtained by measuring the reference pattern, and further calculates anetching pattern from the optical image. The master processor thenretrieves the etchant concentration Ix near a resist edge. The masterprocessor determines the deviation Δ of the measured size of the etchingpattern from the reference pattern, and then retrieves the etchantconcentration Iy at the position where the deviation Δ occurs. Themaster processor determines the relationship between Ix and Iy by meansof the least squares fitting method. The slave processors determinethreshold values, which depend on the etchant concentration Ix in anadjacent region, using the relationship determined by the masterprocessor, and perform correction processing using the threshold values.

In this embodiment, complex effects of the light proximity effect andthe micro loading effect which occur during the optical patterntransferring process and during the etching process can be evaluated,and these effects can be incorporated into the correction process.

EMBODIMENT 20

In the thirteenth embodiment described above, instead of using therelationship between the reference pattern and the optical imagethereof, it is also possible to employ the relationship between thereference mask data and an etching pattern obtained by performing anetching process using a resist pattern transferred from a mask patternformed by performing electron beam exposure according to the referencemask data. In this case, as shown in FIG. 52, a reference pattern isformed by actually performing electron beam exposure according to thereference mask data, and then a resist is exposed to this referencepattern so as to obtain a resist pattern. Furthermore, an etchingpattern is formed by performing an etching process using the resistpattern and the size of the resultant etching pattern is measured. Themaster processor calculates an electron beam exposure pattern from thereference mask data, and further calculates an optical image. Then, themaster processor calculates an etching pattern from the optical image.The master processor then retrieves the etchant concentration Ix near amask edge of the resist pattern. The master processor determines thedeviation Δ of the measured size of the etching pattern from thereference mask data, and then retrieves the etchant concentration Iy atthe position where the deviation Δ occurs. The master processordetermines the relationship between Ix and Iy by means of the leastsquares fitting method. The slave processors determine threshold values,which depend on the etchant concentration Ix in an adjacent region,using the relationship determined by the master processor, and performcorrection processing using the threshold values.

In this embodiment, it is possible to evaluate complex effects of theelectron beam proximity effect, the light proximity effect and the microloading effect, which occur during the electron beam exposure, opticalpattern transferring, and etching processes, and these effects can beincorporated into the correction process.

Alternatively, as shown in FIG. 53, the electron beam exposure may bereplaced by laser beam exposure. In this case, a reference pattern isformed by actually performing laser beam exposure and then a resist isexposed to this reference pattern so as to obtain a resist pattern.Furthermore, an etching pattern is formed by performing an etchingprocess using the resist pattern and the size of the resultant etchingpattern is measured. The master processor calculates a laser beamexposure pattern from the reference mask data, and further calculates anoptical image. The master processor then calculates an etching patternfrom the optical image, and thus the relationship between the calculatedetching pattern and the actual etching pattern is determined. In thisembodiment, it is possible to evaluate complex effects of the laser beamproximity effect, the light proximity effect and the micro loadingeffect, which occur during the laser beam exposure, optical patterntransferring, and etching processes, and these effects can beincorporated into the correction process.

EMBODIMENT 21

The optical image measurement unit 10 shown in FIG. 4 may be constructedwith a plurality of optical systems 151 to 155 as shown in FIG. 15. Thedesign data compressed by the data compression unit 2 is divided into aplurality of data blocks, and these data blocks are measured separatelyin a parallel fashion by the optical systems 151 to 155. Then, themeasured results are combined so as to obtain corrected data. Theparallel processing according to this embodiment results in an increasein the processing speed. For example, if five optical systems are usedas shown in FIG. 15, the processing speed becomes five times faster thanin the case where only one optical system is used.

EMBODIMENT 22

In this embodiment, as shown in FIG. 16, a projection image is formedfrom a mask pattern 161 based on design data, and then, in a transferpattern prediction process, the pattern prediction unit 4 predicts themask edge position assuming that the mask edge is located at theposition where the light intensity is equal to a predefined thresholdI_(TH) and thus predicts the pattern size of a transferred pattern 162formed in a resist or the like on the surface of a wafer. The correctionamount is given by the distance D between the predicted mask edge andthe actual mask edge of the mask pattern 161 based on the design data.The threshold I_(TH) is set to a light intensity, which is 0.20 to 0.40times the light intensity of a flat pattern having no edges. In thisembodiment, the mask edge is predicted on the basis of the thresholdI_(TH) without performing a resist development calculation. This resultsin a reduction in the processing time.

EMBODIMENT 23

In the previous embodiment 22, the threshold I_(TH) may be adjusteddepending on the light intensity in areas near sides of a patternelement to be corrected. For example, a mask pattern 171 shown in FIG.17A has a narrow light transmission pattern element. Therefore, thelight intensity near the sides (edges) to be corrected becomes lowerthan in the case of a wider light transmission pattern element. In thiscase, the threshold I_(TH) is set to a higher value. In contrast, whenthe light transmission part of a pattern element is wide as in maskpatterns 173, 181, and 183 shown in FIGS. 17B, 18A, and 18B,respectively, the light intensity near sides (edges) to be corrected islarge enough. Therefore, the threshold I_(TH) is set to a lower value inthis case. In this embodiment, transferred patterns 172, 174, 182, and184 are predicted, taking into account the conditions near the sides tobe corrected thereby quickly achieving high accuracy pattern prediction.

EMBODIMENT 24

In embodiment 22, the threshold I_(TH) may be adjusted depending on thetwo-dimensional light intensity distribution near sides to be corrected.For example, when a rectangular pattern such as that shown in FIG. 33 isto be corrected, the light intensity distribution near a point Pa at acorner of the rectangular pattern 330 is different from that near apoint Pb on a side. Therefore, the correction amount for the point Pa isdifferent from that for the point Pb. To avoid the above problem, aplurality of monitor points Pm are disposed near the points Pa and Pbwhereby two-dimensional light intensity distribution is monitored and itis detected whether the points Pa and Pb are located at a corner or on aside. If it is detected that a point is located at a corner, thecorrection amount D4 should be greater than the correction amount D3 fora point on a side so as to cancel the effects of etching, development,and the like. Therefore, the threshold I_(TH) is set to a low value inthis case. In this embodiment, the two-dimensional conditions of apattern are taken into account in the pattern prediction so that highaccuracy pattern prediction is achieved.

EMBODIMENT 25

In embodiment 22 the threshold I_(TH) may be adjusted depending onwhether there is some pattern element near a side to be corrected. Forexample, in the case of a mask pattern 351 shown in FIG. 35A, there areno pattern elements near a side 351 a to be corrected. In contrast, inthe case of a mask pattern 353 shown in FIG. 35B, there is a patternelement near a side 353 a to be corrected. In this case, the lightintensity in an area on the right of the side 353 a becomes lower. Toavoid this problem, monitor points Pm are disposed on the right and leftof a side of a pattern element to be corrected so as to detect whetherthere is another pattern element near the side. In the case of the maskpattern 351, the sum of the light intensities at the right and leftmonitor points Pm has a large value, and thus it is concluded that thereis no pattern element near the side under the consideration and thethreshold I_(TH) is set to a large value. On the other hand, in the caseof the mask pattern 353, the sum of the light intensities at the rightand left monitor points Pm has a small value, and thus it is concludedthat there is another pattern element near the side under theconsideration and the threshold I_(TH) is set to a small value. Thisoffers further high accuracy in the pattern prediction.

EMBODIMENT 26

In embodiment 22 the threshold I_(TH) may also be adjusted depending onthe light intensity of an optical image obtained under a defocusingcondition relative to the light intensity of the optical image obtainedunder a best focusing condition. As shown in FIG. 36, the lightintensity Id of an optical image under a defocusing condition iscalculated, and it is determined whether the light intensity Id isgreater than the light intensity Ib of an optical image under a bestfocus condition. If the light intensity Id under the defocusingcondition is greater than the light intensity Ib under the best focuscondition, the size of a resist pattern will become small. Therefore,the threshold I_(TH) is set to a low value so as to prevent the resistpattern size from becoming small. On the other hand, if the lightintensity Id under the defocusing condition is smaller than the lightintensity Ib under the best focus condition, the resist pattern sizewill become larger. In this case, the threshold I_(TH) is set to a largevalue so as to prevent the resist pattern size from becoming large.Thus, in this embodiment, the focusing margin is effectively expanded.

EMBODIMENT 27

In embodiment 22 the threshold I_(TH) may be adjusted depending on theslope of the projection image near the predicted mask edge. Afterward,the mask edge is predicted again using the new threshold value I_(TH)obtained by the above adjustment. As shown in FIGS. 19A and 19B,thresholds I_(TH) are adjusted depending on the slopes of projectionimages near the mask edges of mask patterns 191 and 193 obtained in thefirst prediction. The edges of projection images are predicted againusing the new thresholds I_(TH) thereby predicting transferred patterns192 and 194. In this embodiment, the slope of a projection image, thatis the slope of light intensity, can be taken into account in thepattern prediction. As a result, it is possible to achieve high accuracypattern prediction.

EMBODIMENT 28

In this embodiment, as shown in FIG. 20, after generating a projectionimage on the basis of a mask pattern 201, the pattern prediction unit 4simulates the development process of a resist on the surface of a wafer.A transferred pattern 202 is then predicted from the simulation result.In this embodiment, the variations in the process conditions such as anexposure amount and development time can be easily taken into account inthe pattern prediction so that high accuracy pattern prediction can beachieved.

EMBODIMENT 29

In this embodiment, as shown in FIG. 21, after generating a projectionimage on the basis of a mask pattern 211, the pattern prediction unit 4converts the projection image to a distribution 212 of development timerequired to develop the resist on the surface of a wafer. The patternprediction unit 4 further integrates the distribution 212 in aone-dimensional fashion thereby performing quasi-development. Atransferred pattern 213 is then predicted from the result of thequasi-development. In this embodiment, as described above, patternprediction can be performed more easily and more quickly than predictionon the basis of a simulation of resist development.

EMBODIMENT 30

In the transfer pattern prediction step after generating a projectionimage from a mask pattern based on design data, the threshold I_(TH) maybe adjusted depending on the reflectivity of an underlying substratecoated with a resist which is to be formed into a pattern. As shown inFIG. 37A, in the case where an underlying substrate 371 is made of amaterial such as WSi having low reflectivity, the light reflected by thesubstrate 371 has less influence on the exposure, and therefore the sizeof the resist pattern becomes greater when a positive-type resist isused. On the other hand, if an underlying substrate 372 is made of amaterial such as Al having a high reflectivity, the light reflected bythe substrate 372 makes a considerable contribution to exposure andtherefore the size of the resist patter becomes smaller when apositive-type resist is used. The threshold I_(TH) is set to a highvalue for an underlying substrate having a low reflectivity as in thecase of FIG. 37A, and the threshold I_(TH) is set to a low value for anunderlying substrate having a high reflectivity as in the case of FIG.37B. In this embodiment the effect of the reflectivity of the underlyingsubstrate is taken into account in the prediction of a transferredpattern and thus it is possible to achieve high accuracy and highprocessing speed in the pattern prediction.

EMBODIMENT 31

In the transfer pattern prediction step after generating a projectionimage from a mask pattern based on design data, the threshold I_(TH) maybe adjusted depending on steps formed on an underlying substrate coatedwith a resist in which a pattern is to be formed. In the example shownin FIG. 38A, an opening 382 and steps are formed on an under lyingsubstrate 381 and the opening 382 and the steps are covered with aresist 383 wherein the thickness of the resist in the opening 382 isgreater than that of the other portions. In such a case, the thresholdI_(TH) for the thick area is set to a large value. In this embodiment,the effects of steps on an underlying substrate and the local variationsin resist thickness are taken into account in the prediction of atransferred pattern and thus it is possible to achieve high accuracy inthe pattern prediction.

EMBODIMENT 32

In the transfer pattern prediction step after generating a projectionimage from a mask pattern based on design data, the threshold I_(TH) maybe adjusted depending on halation produced on the surface of anunderlying substrate coated with a resist into which a pattern is to beformed. For example, there is a large step 393 at the boundary between amemory cell area 391 and a peripheral circuit area 392 as shown in FIG.39A. If bit lines 394 are formed 50 that they extend from the memorycell area 391 to the peripheral circuit area 392 across the step 393,halation occurs at the step 393 and a part of light is reflected in ahorizontal direction as shown in FIG. 39B. In view of that fact, thethreshold I_(TH) for the area near the step is set to a lower value thanfor the other areas. In this embodiment the effect of halation at stepson an underlying substrate is taken into account in the prediction of atransferred pattern and thus it is possible to achieve high accuracy inthe pattern prediction.

EMBODIMENT 33

The optical image calculation unit 3 of the embodiment 2 may calculate aprojection image as follows. First, light intensities at predefined meshpoints are calculated. Then, as shown in FIG. 22, the light intensity Iat an arbitrary point P (x, y) is calculated from the already-determinedlight intensities at four neighboring points Pi(xi, yi) (i=1, 2, 3, 4)by means of interpolation according to the following equation:

I=Σi(Wi·Ii)

where Wi=(1−|xi−x |)(1−|yi−yl). Thus, according to this method ofcalculating a projection image, it is possible to calculate the lightintensity at an arbitrary point, even at a point on a boundary line ofthe mesh. As a result, it is possible to obtain a high-accuracyprojection image.

EMBODIMENT 34

In the data correction processing in embodiment 2 or 3, the correctionunit 6 divides each side of a pattern element 231 shown in FIG. 23A intoa plurality of segments as shown in FIG. 23B, then performs correctionsseparately on each segment. In this embodiment, each dividing point 232has two data for individual segments sharing that dividing point so thateach segment can be corrected independently without affecting adjacentsegments. Thus, this embodiment offers high-accuracy correction.

EMBODIMENT 35

In the data correction process, the correction unit 6 corrects each sideof a pattern element which should be corrected in a direction which islimited only to the direction perpendicular to each side. For example, aside 242 of a pre-corrected pattern element 241 shown in FIG. 24A iscorrected in a direction perpendicular to this side 242 so as to obtaina corrected pattern element 243 having a side 244. In this technique,correction produces no slanted sides and thus data can be compressedeffectively and electron beam exposure can be performed at a highprocessing speed.

EMBODIMENT 36

In the data correction process, if the edge gradient of the projectionimage of a pattern is steeper than a predetermined degree, thecorrection unit 6 may skip that side (edge) without performing acorrection. For example, if a mask pattern 252 includes thin patternelements arranged close to each other as shown in FIG. 25, thetransferred pattern 252 becomes unclear and thus inaccurate. In thiscase, the edge gradient of the projection image of the mask pattern 251becomes less steep. In this embodiment, as described above, when theedge gradient of the projection image of a pattern is steeper than apredetermined degree, the side is skipped without being subjected tocorrection thereby preventing invalid correction. This offers highreliability in the light proximity correction.

EMBODIMENT 37

In the data correction process, if the light intensity of the projectionimage of a pattern is less than a predetermined threshold for a certainside of the pattern, the correction unit 6 may skip that side (edge)without performing a correction. In FIG. 26A, for example, the side 263shown in the circle 262 is located inside a pattern element 261 andtherefore this side 263 does not require light proximity correction andthis side 263 should be skipped in the correction process. In such acase, the light intensity of the projection image of the 263 is very lowas shown in FIG. 26B because the side 262 is located inside the patternelement 261. In this embodiment if the light intensity of the projectionimage of a side of a pattern is less than a threshold I₀, the side isskipped in the correction process so that invalid correction isprevented and high reliability is achieved in the light proximitycorrection.

EMBODIMENT 38

In the data correction process, if the correction unit 6 detects that acorrection is greater than a predefined upper limit, the correction unit6 considers the correction to be invalid and employs a value equal tothe upper limit as the correction. For example, as shown in FIG. 27A, ifthe correction amount D1 for a side 272 of a pattern element 271 isgreater than an upper limit D2, the correction amount D1 is replaced bythe upper limit D2 so that the side 272 becomes a side 274 in thecorrected pattern element 273 as shown in FIG. 27B. This prevents aninvalid correction and thus offers high reliability in the lightproximity correction.

EMBODIMENT 39

In the data correction process, the correction unit 6 may removeredundant points which lie on the same line after correcting a side of apattern. For example, as shown in FIG. 28A, after a correction process,a pattern 281 has redundant points 282 to 285 lying on lines, whereinthese redundant points 282 to 295 are no longer necessary after thecompletion of the correction process. Therefore, the correction unit 6removes these points 282 to 285 and produces a pattern such as thatshown in FIG. 28B. Thus, data can be compressed in an effective fashion,and iterative calculations in the correction process can be performed ina short time.

EMBODIMENT 40

In step S6 in the embodiment 2 or 3, if the correction amount is notwithin the allowable range, a projection image is generated andcorrection is performed again. In this embodiment, instead of judgingthe correction amount each time a side is corrected and iterating thecorrection process, the correction amount is judged after all sides havebeen corrected separately, and the correction procedure is repeated asrequired. This results in an increase in the correction processingspeed. Furthermore, since each side is corrected independently, there islittle possibility that the correction will become asymmetric, and thusit is possible to achieve high reliability in the correction process.

EMBODIMENT 41

In embodiment 2 or 3, after dividing the design data into a plurality ofdata blocks and calculating the correction amount for each data block,the correction amount is evaluated. If it is detected that thecorrection amount for a certain data block is not within an allowablerange, then such a data block may be extracted and stored in a separatefile whereas the corrected data of the data blocks which have succeededin obtaining a correction amount within the allowable range is output.For example, as shown in FIG. 54, after performing pre-processing on themask data, a resist pattern is predicted by means of opticalcalculation, and the predicted resist pattern is evaluated by comparingit with the mask data.

That is, the difference between the size of the predicted pattern andthe size designated by the mask data is determined as the correctionamount. If the correction amount is greater than 10% of the minimum sizefor example, 0.3 μm, then data blocks having such a correction amountare extracted and stored in a separate file.

This makes it possible to extract only those regions which needcorrection or have too small a process margin from an LSI patternincluding a huge amount of data. This technique is especially useful forrandom logic circuits to improve the development efficiency. The datawhich has been extracted for the correction in the above-describedmanner is subjected to pre-processing using optical parameters and thecalculated projection image and the corresponding mask data aredisplayed. Referring to the corrected data of the data blocks which havealready succeeded in achieving a correction amount within the allowablerange, it is determined whether or not correction is needed judging fromthe displayed projection image. If correction is needed, correction isperformed manually, and the mask data and the projection image aredisplayed again for re-evaluation. The manual correction and thedisplaying of the mask data and the projection image are performedrepeatedly until it is determined that no further correction is needed.When it is concluded that no further correction is needed, the resultantcorrected data are output.

The, the present invention provides not only a full-automatic lightproximity correction system in which correction is performed from blockto block, but also a semi-automatic light proximity correction systemwith which an operator can manually correct the extracted data. This isespecially useful to achieve effective correction when a fully automaticsystem is not good enough, particularly for a special pattern, or whenit is desirable to monitor the optical image during a correctionprocess.

EMBODIMENT 42

In embodiment 2 or 3, as described in FIG. 40A, after dividing thedesign data into a plurality of data blocks and disposing a buffer area402 around each data block 401, a correction process is performed. Afterthat, in the data expansion process (step S7), if the buffer area aroundeach data block is removed as shown in FIG. 40B and the corrected dataincluding no buffer area is stored, then the data can be expanded asshown in FIG. 40C with more effectively compressed corrected data.

What is claimed is:
 1. A method of forming a pattern on and processing awafer comprising: generating pattern data for a circuit pattern of anintegrated circuit; correcting the pattern data to compensate for thelight proximity effect that occurs during transferring the circuitpattern to a wafer using light by forming an optical projection image ofthe pattern data, predicting the size of the pattern that will betransferred to the wafer on the basis of the projection image,calculating a difference between the size of the pattern predicted to betransferred and the size of the pattern data, and correcting the patterndata by an amount equal to the difference; preparing a mask using thecorrected data to produce a mask pattern; exposing a wafer to lightpassing through the mask pattern, thereby transferring the mask patternto the wafer; and processing the wafer using the mask patterntransferred to the wafer.
 2. The method of claim 1 comprisingdetermining whether the correction is within an allowable range andreforming the optical image if the correction is not within theallowable range.
 3. The method of claim 1 comprising: predicting a maskedge on the optical image by employing a predetermined light intensityas a threshold value; adjusting the threshold value depending on thegradient of the projection image and the predicted mask edge; andpredicting a mask edge using the adjusted threshold value, therebypredicting the size of the pattern that will be transferred to thewafer.
 4. A method of fabricating a semiconductor device comprising:forming a mask by preparing pattern data for a circuit pattern to betransferred to an underlying substrate; and correcting the pattern datato compensate for the light proximity effect occurring duringtransferring the circuit pattern to a resist using light by forming anoptical projection image of the pattern data; predicting size of thecircuit pattern that will be transferred to the resist based on theoptical projection image; and calculating a difference between the sizeof the circuit pattern predicted to be transferred and the size of thecircuit pattern, and generating corrected data used for producing a maskpattern of a mask; forming a resist on an underlying substrate; exposingthe resist to light through the mask to transfer the mask pattern of themask to the resist; developing the resist to form a patterned resist;and etching the underlying substrate using the patterned resist.
 5. Themethod of claim 4, wherein predicting the size of the circuit patterncomprises: predicting location of a mask edge on the optical projectionimage by employing a threshold light intensity depending on a gradientof the optical projection image and the mask edge predicted; andpredicting a mask edge using the threshold light intensity afteradjustment.
 6. A method of fabricating a semiconductor devicecomprising: forming a mask by preparing pattern data for a circuitpattern to be transferred to an underlying substrate; correcting thepattern data to compensate for the light proximity effect occurringduring transferring the circuit pattern to a resist using light, andgenerating corrected data used for producing a mask pattern of a mask;determining whether correction of the pattern data is within anallowable range; and correcting the pattern data again if the correctionis not within the allowable range; forming a resist on an underlyingsubstrate; exposing the resist to light through the mask to transfer themask pattern of the mask to the resist; developing the resist to form apatterned resist; and etching the underlying substrate using thepatterned resist.
 7. A method of fabricating a semiconductor devicecomprising: forming a mask by preparing pattern data for a circuitpattern to be transferred to an underlying substrate; correcting thepattern data to compensate for the light proximity effect occurringduring transferring the circuit pattern to a resist using light byadding an auxiliary pattern to the circuit pattern, and generatingcorrected data used for producing a mask pattern of a mask; forming aresist on an underlying substrate; exposing the resist to light throughthe mask to transfer the mask pattern of the mask to the resist;developing the resist to form a patterned resist; and etching theunderlying substrate using the patterned resist.